WASHINGTON—A man who had been forced out of the military after a 2010 gun arrest opened fire inside a Navy building Monday morning, killing 12 people and injuring about eight more as he sprayed bullets into a cafeteria of unsuspecting military workers, officials said.

Authorities said the alleged gunman, Aaron Alexis of Fort Worth, Texas, was killed in a shootout with police at the scene, but that wasn't the end to a chaotic day in the nation's capital that saw security officials lock down military buildings and the U.S. Senate, and cancel the Washington Nationals game scheduled later in the evening.

Hours after the shooting, Police Chief Cathy Lanier warned there could be two additional gunmen, but later investigators decided Mr. Alexis was likely the sole gunman.

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People stream out of a building at the Washington, D.C., Navy Yard with their hands up after a mass shooting that left at least a dozen dead.
Alex Wong/Getty Images

Prior to a speech recognizing the five-year anniversary of the 2008 financial crisis, President Barack Obama gave a short statement on the Monday morning shooting spree at Washington, D.C.'s, Navy Yard.

In a city that has greatly toughened its security measures since the 2001 terror attacks, when a plane slammed into the Pentagon, the incident at the U.S. Navy Yard shows that significant vulnerabilities remain, even at a guarded military facility.

Patricia Ward, a logistics management specialist, was in the building cafeteria when she said she heard a "pop, pop, pop" from above as a gunman on the fourth floor fired into an atrium on people getting their morning coffee below. The gunman continued to fire as Ms. Ward and others rushed out of the building.

"We just started running," Ms. Ward said.

President Barack Obama, who was briefed as the situation unfolded, said, "These are men and women who were going to work, doing their job protecting all of us. They're patriots. And they know the dangers of serving abroad, but today they faced the unimaginable violence that they wouldn't have expected here at home." He pledged a thorough investigation.

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Navy workers were gunned down, allegedly by Aaron Alexis, in a 2010 booking photo; he was killed in a shootout.
Associated Press

The police department released the names of seven of the 12 victims, and said that none are military personnel. They are Michael Arnold, 59 years old; Sylvia Frasier, 53; Kathy Gaarde, 62; John Roger Johnson, 73; Frank Kohler, 50; Bernard Proctor, 46, and Vishnu Pandit, 61. The department has also said that eight people were injured.

The incident was the third mass shooting in the country in little more than a year. In December 2012, a gunman shot 20 youngsters and six staff members at an elementary school in Newtown, Conn., and in July 2012, 12 people were shot to death at a movie theater in Aurora, Colo.

Mr. Alexis, 34 years old, was identified by fingerprints taken off his corpse, officials said.

Investigators linked a shotgun Mr. Alexis carried to a purchase he allegedly made last week in Lorton, Va., law-enforcement officials said. Investigators theorize he used the shotgun to shoot a security officer, then took at least one other weapon, a rifle, from that officer or another victim. Witnesses reported seeing Mr. Alexis firing a rifle, and officials said he also may have carried a second long gun and a handgun.

The Federal Bureau of Investigation said late Monday that Mr. Alexis gained access to the Navy Yard with a valid pass obtained as part of his contractor work.

Mr. Alexis was employed by The Experts, a Fort Lauderdale, Fla.-based subcontractor for Hewlett-Packard Co.'s H-P Enterprise Services unit. Thomas Hoshko, CEO of The Experts, said Mr. Alexis had worked for the company on a U.S. base in Japan from September 2012 to January 2013 without incident, and had been rehired in July for a project at the Navy yard. He underwent a new security background review and his secret security clearance had been re-approved, Mr. Hoshko said.

He said he didn't know if Mr. Alexis had already started working on the base. "I'm as perplexed as anyone: how can this guy have a clearance if he had a history or problems?" he said.

"This guy must have snapped," he said.

The Experts has about 800 employees, and Mr. Hoshko said he never met Mr. Alexis.

Photos

Emergency vehicles and law enforcement personnel respond to a reported shooting at an entrance to the Washington Navy Yard Monday in Washington, DC. Getty Images

Lt. Lauren Dempsey, a Navy spokeswoman, said workers inside Building 197 were ordered to remain in place as officials pursued the shooter.

The building houses the Naval Sea Systems Command, and about 3,000 people work in the headquarters unit. The command is in charge of engineering, procuring and building Navy ships and submarines, and is the largest of the Navy's five system commands. Overall, the command employs 60,000 people.

According to witnesses and police, the gunman took a perch at a fourth-floor overlook, firing onto the cafeteria on the first floor. Initially, many of those in the cafeteria didn't realize they were under fire. As people began collapsing with gunshot wounds, people scrambled for cover, said authorities and witnesses, who added that the shooter also fired on people he came across in hallways.

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A witness to the shootings at the Washington Navy Yard Monday morning recounts to reporters what she saw and heard.

An alarm sounded, alerting employees to evacuate. Police responded and began searching room to room. City and federal park police officers eventually found the suspect in the building and began trading fire with him. He died in the shootout, authorities said.

Authorities said they had yet to determine a motive, but had found nothing to suggest a connection to terrorism.

A U.S. official said Mr. Alexis had enlisted in the Navy in 2007 and had been an active reservist, but was forced out in early 2011 after a gun incident at his apartment. He had been serving in Fort Worth at the time, according to his military work history. Police records also indicate Mr. Alexis was arrested in Seattle in May 2004 and charged with using a pistol to shoot the tires on the car of a construction worker, but no charges were filed in court, said a clerk at King County District Court in Seattle.

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A defense official said Mr. Alexis was pushed out of the military because of repeated incidents and arrests. "There is no question there was a pattern of misconduct while in the Navy reserves," the official said.

Mr. Alexis, officials said, wasn't dishonorably discharged from the Navy. A dishonorable discharge would have prohibited him from legally purchasing a gun.

The FBI made a public appeal for information about Mr. Alexis, asking them to call 1-800-CALL-FBI. "We are looking to learn everything we can about his recent movements, his contacts and his associates,'' said Valerie Parlave, head of the FBI's local office.

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A woman reunited with her husband who was inside.
Reuters

For the past three years, Mr. Alexis had attended the Wat Busaya Dhammavanaram Meditation Center, a Buddhist Thai temple in Fort Worth, members said. Kasem Pundisto, a monk at the temple, said Mr. Alexis told him he was troubled, though Mr. Alexis didn't tell him why.

"When he came here and prayed and chanted, that made him feel better," said Mr. Pundisto.

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